The overall goal of this proposal is the induction of tolerance simultaneously to both renal and pancreatic islet transplants across an allogeneic barrier in baboons. The studies are based upon the following previous observations: 1) tolerance to fully mismatched renal allografts can be achieved in juvenile miniature swine by a short course of high-dose tacrolimus, and preliminary data indicate that this methodology is also successful in juvenile baboons;2) in contrast to free islet grafts, composite "islet kidneys" (I-K), prepared by transplantation of autologous swine islets under the kidney capsule two months prior to transplantation of the composite organ into nephrectomized, pancreatectomized allogeneic recipients, restore euglycemia immediately and maintain both renal and islet function long-term;and 3) tolerance to renal allografts can be achieved in adult animals by induction of mixed hematopoietic chimerism. We propose here to extend these studies to the induction of tolerance to I-K in baboons, with the intent of developing a clinically relevant treatment protocol for end stage diabetic nephropathy. Specifically, we will: 1) Establish a non-human primate model of renal allograft tolerance in juvenile baboons;2) Assess the association of biologic and molecular markers with tolerance and rejection in baboons undergoing tolerance-induction protocols;3) Test the ability of composite islet-kidney transplants to treat both diabetes and renal failure in nephrectomized, juvenile baboons, made diabetic through STZ treatment;and 4) Extend treatment of diabetes and renal failure by I-K transplantation to adult baboons using tolerance induction through a mixed chimerism approach and assess the validity of biologic and molecular biomarkers of tolerance induction developed in Aim 2 for assessment of tolerance induction. We anticipate that the combination of tolerance induction and the use of pre-vascularized islets in these approaches could provide a new and effective treatment modality for patients with type I diabetes and end-stage renal disease.